Field of the Invention
The present invention relates to a polymer nanofiber structural body having a plurality of pore structures therein and a composite obtained by using the structural body, and methods of producing the structural body and the composite.
Description of the Related Art
In recent years, industrial utilization of fine particles has become active. Meanwhile, a particle-collecting apparatus for collecting fine particles scattered in air or dispersed in a liquid has been needed. A polymer nanofiber structural body in which polymer nanofibers are integrated and three-dimensionally intertwined with each other typified by a polymer nanofiber sheet has been attracting attention as a material for such particle-collecting apparatus.
Unlike general fibers to be used in a nonwoven fabric and the like, each of the polymer nanofibers has a diameter of several micrometers or less. Accordingly, the polymer nanofiber structural body is drastically superior to a structural body including the general fibers because of the following reason. Even when the polymer nanofibers are integrated, an enormous specific surface area, a nanosize continuous pore structure, and a low density are obtained. By virtue of those properties, new functions such as a mechanical strength, reactivity, electrical and optical characteristics, and the permeability of the inside of the structural body can be imparted. In particular, when the pore structure is utilized, a pore diameter of the order of submicrons is obtained and hence the pore structure is suitable for the collection of fine particles. Further, each of the polymer nanofibers uses an organic compound as a parent material and hence is lightweight. In addition, the polymer nanofibers can be produced with ease and at a low cost.
Meanwhile, in order to selectively collect fine particles having different sizes, it has been necessary that the polymer nanofiber structural body have a plurality of pore structures therein. In addition, such a polymer nanofiber structural body that the ratio of a polymer nanofiber portion, i.e., the amount of polymer nanofibers present in the structural body is large has been needed for increasing the amount of the fine particles to be collected.
Japanese Patent Application Laid-Open No. 2012-223254 discloses a construction provided with a plurality of pore structures by integrating a nanofiber layer on a macrofiber layer. However, in the structural body disclosed in Japanese Patent Application Laid-Open No. 2012-223254, adhesion between the two fiber layers is low. Accordingly, the structural body may peel at an interface between the layers in the case where the structural body is used in a bent state like the case where the structural body is bonded to a curved surface. In view of the foregoing, Japanese Patent Application Laid-Open No. 2012-219384 discloses a construction in which interfacial adhesiveness between a base material layer and a nanofiber layer is improved by forming a bead-like structural body in a nanofiber upon integration of the nanofiber layer on the base material layer.
The composite disclosed in Japanese Patent Application Laid-Open No. 2012-219384 has high adhesiveness at an interface between the base material layer and the nanofiber layer. However, the clogging of a pore structure occurs owing to the bead-like structural body and hence the efficiency with which fine particles are collected reduces in some cases.